1. Field of the Invention
The present invention relates to a system for generating and using electrical energy in a vehicle tyre and a tyre equipped with this system.
More specifically, the present invention relates to a system for generating electrical energy while a vehicle is in motion, this energy also being able to be stored for use in the said tyre even when the vehicle is stationary.
2. Description of the Related Art
U.S. Pat. No. 4,504,761 discloses an electricity generating apparatus comprising                a motor vehicle having an electrical system comprising a battery and a plurality of assemblies comprising a wheel and a tyre having a rubber envelope comprising a first annular band and a second annular band that has a plurality of projections positioned close to the first band so as to move towards it in response to rolling movements of the tyre; and        means for generating electricity in response to movements of the motor vehicle along a road comprising                    a multiplicity of piezoelectric elements fixed to the first band and positioned close to the projections so as to engage with them during the rolling movement of the tyre in order to generate electricity in response to the rolling movement of the tyres with respect to the road; and            means of interconnection of the piezoelectric elements in a circuit with the battery to supply electrical energy, generated by the piezoelectric elements, to the battery, the said means having output conductors.                        
The electricity generating system in that patent exhibits many disadvantages. The bands carrying the piezoelectric elements and the projections which activate them require the existence of a sort of chamber in the tyre. This requires a profound modification of the structure of the tyre and significantly increases the costs of manufacture. It also increases the weight of the tyre and thereby adversely affects its performance, such as rolling resistance and comfort.
In addition, the fitting of the various piezoelectric elements in their band and the formation of the inductive systems necessary to transmit the electrical energy produced to the battery of the motor vehicle are very complex and expensive.
It is also known that it has been proposed that various types of sensors be installed in the tyre, e.g. pressure, temperature, force, velocity sensors an the like, to monitor and control the performance of the tyre and/or of the vehicle. These systems however require an electrical power supply system for the operation of the sensor and/or of the transmitter which transfers out the data and information collected by the sensor.
The power supply systems proposed hitherto are essentially of two types.
The first type consists of inductive systems or sliding-contact systems such as that required in U.S. Pat. No. 4,504,761, except that the electrical energy is transferred from the vehicle battery to a sensor and/or transmitter located in the tyre. However, as we have already seen, these systems have the drawback of being very complicated and expensive.
The second type meanwhile consists of a cell mounted inside the tyre. However, even the most sophisticated and expensive cells eventually run down and replacing them with a new cell inside the tyre will be a nuisance and expensive for the user of the vehicle.
The industry is therefore still highly conscious of the need for a system able to power a sensor and/or a transmitter located inside a tyre of a vehicle wheel that will be simple, cheap and not inconvenience the user of the vehicle.